using System.Globalization;
using System.Xml.Linq;

namespace VideoDownloader.Core.Dash;

/// <summary>
/// MPD(DASH 매니페스트) 파서. 클리어(비DRM) 콘텐츠의 최고화질 비디오(+오디오) 트랙을 구성.
/// 지원: SegmentTemplate($Number$/SegmentTimeline/duration) + SegmentList + BaseURL 누적.
/// 미지원: DRM(ContentProtection), SegmentBase(바이트레인지), 다중 Period.
/// 네임스페이스 무관(LocalName 기반 조회).
/// </summary>
public static class DashParser
{
    public static DashManifest? Parse(string xml, Uri mpdUrl, bool lowestRep = false)
    {
        XDocument doc;
        try { doc = XDocument.Parse(xml); }
        catch { return null; }
        var mpd = doc.Root;
        if (mpd == null || mpd.Name.LocalName != "MPD") return null;

        var period = Child(mpd, "Period");
        if (period == null || Child(period, "ContentProtection") != null) return null; // DRM

        var mpdBase = Combine(mpdUrl, Val(Child(mpd, "BaseURL")));
        var periodBase = Combine(mpdBase, Val(Child(period, "BaseURL")));

        // 세그먼트 수 산정용 기간: Period@duration > MPD@mediaPresentationDuration > MPD@duration
        var periodSec = ParseDuration(Attr(period, "duration"));
        if (periodSec <= 0) periodSec = ParseDuration(Attr(mpd, "mediaPresentationDuration"));
        if (periodSec <= 0) periodSec = ParseDuration(Attr(mpd, "duration"));

        DashTrack? video = null, audio = null;
        foreach (var s in Children(period, "AdaptationSet"))
        {
            if (Child(s, "ContentProtection") != null) continue; // DRM 셋
            var ct = (Attr(s, "contentType") ?? Attr(s, "mimeType") ?? "").ToLowerInvariant();
            var track = BuildTrack(s, periodSec, periodBase, lowestRep);
            if (track == null) continue;
            if (video == null && ct.Contains("video")) video = track;
            else if (audio == null && ct.Contains("audio")) audio = track;
            else if (video == null) video = track; // contentType 없으면 첫 트랙을 비디오로
        }

        if (video == null) return null;
        return new DashManifest { Video = video, Audio = audio, DurationSec = periodSec };
    }

    /// <summary>하나의 AdaptationSet 에서 최고(또는 최저)화질 비DRM 표현을 골라 세그먼트 묶음 생성.</summary>
    private static DashTrack? BuildTrack(XElement set, double periodSec, Uri periodBase, bool lowestRep)
    {
        var setBase = Combine(periodBase, Val(Child(set, "BaseURL")));
        var setTemplate = Child(set, "SegmentTemplate");

        XElement? rep = null; long bestBw = -1;
        foreach (var r in Children(set, "Representation"))
        {
            if (Child(r, "ContentProtection") != null) continue;
            var bw = (long?)r.Attribute("bandwidth") ?? 0;
            if (rep == null || (lowestRep ? bw < bestBw : bw > bestBw)) { bestBw = bw; rep = r; }
        }
        if (rep == null) return null;

        var repBase = Combine(setBase, Val(Child(rep, "BaseURL")));
        var tmpl = Child(rep, "SegmentTemplate") ?? setTemplate;
        var repId = Attr(rep, "id") ?? "0";
        var bwStr = bestBw.ToString();

        // SegmentList
        var segList = Child(rep, "SegmentList") ?? Child(set, "SegmentList");
        if (segList != null)
        {
            var segs = new List<DashSegment>(); int i = 0;
            foreach (var su in Children(segList, "SegmentURL"))
            {
                var m = Attr(su, "media");
                if (m != null) segs.Add(new DashSegment(Combine(repBase, m), i++));
            }
            var init = Attr(segList, "initialization");
            return new DashTrack { InitUrl = init != null ? Combine(repBase, init) : null, Segments = segs };
        }

        // SegmentTemplate
        if (tmpl != null)
        {
            var initT = Attr(tmpl, "initialization");
            var mediaT = Attr(tmpl, "media");
            if (string.IsNullOrEmpty(mediaT)) return null;
            var startNumber = (long?)tmpl.Attribute("startNumber") ?? 1;
            var tmplBase = Combine(repBase, Val(Child(tmpl, "BaseURL")));
            Uri? initUrl = initT != null ? Combine(tmplBase, Subst(initT, repId, bwStr, startNumber, 0)) : null;

            var segs = new List<DashSegment>();
            var timeline = Child(tmpl, "SegmentTimeline");
            if (timeline != null)
            {
                // #8 $Time$ 는 미디어 시작시간(t/d 누적) 이지 세그먼트 번호가 아님(ISO/IEC 23009-1).
                //    t 속성은 타임라인을 해당 절대시각으로 재설정.
                // #9 r=-1 은 "Period 끝까지 반복" — count=r+1=0 으로 0개를 내던 버그 수정.
                var timescale = (long?)tmpl.Attribute("timescale") ?? 1;
                long endTime = periodSec > 0 ? (long)Math.Ceiling(periodSec * timescale) : long.MaxValue;
                long number = startNumber; int idx = 0; long time = 0;
                const long MaxSegs = 200000; // 폭주 방지 상한
                foreach (var se in Children(timeline, "S"))
                {
                    var tAttr = (long?)se.Attribute("t");
                    if (tAttr.HasValue) time = tAttr.Value;   // t: 타임라인 재설정(절대 시각)
                    var d = (long?)se.Attribute("d") ?? 0;
                    var r = (long?)se.Attribute("r") ?? 0;
                    if (d <= 0) continue;
                    if (r < 0)
                    {
                        // r=-1: 다음 세그먼트 시작이 Period 끝(endTime) 에 달하거나 넘으면 정지.
                        while (idx < MaxSegs && time < endTime)
                        {
                            segs.Add(new DashSegment(Combine(tmplBase, Subst(mediaT, repId, bwStr, number, time)), idx++));
                            number++; time += d;
                        }
                    }
                    else
                    {
                        for (long k = 0; k < r + 1 && idx < MaxSegs; k++)
                        {
                            segs.Add(new DashSegment(Combine(tmplBase, Subst(mediaT, repId, bwStr, number, time)), idx++));
                            number++; time += d;
                        }
                    }
                }
            }
            else
            {
                var timescale = (long?)tmpl.Attribute("timescale") ?? 1;
                var duration = (long?)tmpl.Attribute("duration") ?? 0;
                if (duration > 0)
                {
                    long total = periodSec > 0 ? (long)Math.Ceiling(periodSec * timescale / (double)duration) : 0;
                    if (total <= 0) total = 1;
                    for (long n = 0; n < total; n++)
                        segs.Add(new DashSegment(Combine(tmplBase, Subst(mediaT, repId, bwStr, startNumber + n, n * duration)), (int)n));
                }
            }
            return new DashTrack { InitUrl = initUrl, Segments = segs };
        }

        // BaseURL 단일 파일 표현
        var repBaseOnly = Val(Child(rep, "BaseURL"));
        if (!string.IsNullOrEmpty(repBaseOnly))
            return new DashTrack { InitUrl = null, Segments = new[] { new DashSegment(Combine(setBase, repBaseOnly), 0) } };

        return null;
    }

    private static XElement? Child(XElement? p, string local) =>
        p?.Elements().FirstOrDefault(e => e.Name.LocalName == local);

    private static IEnumerable<XElement> Children(XElement? p, string local) =>
        p?.Elements().Where(e => e.Name.LocalName == local) ?? Enumerable.Empty<XElement>();

    private static string? Attr(XElement e, string n) => (string?)e.Attribute(n);
    private static string? Val(XElement? e) => e == null ? null : e.Value.Trim();

    /// <param name="number">$Number$ 값(세그먼트 순번)</param>
    /// <param name="time">$Time$ 값(미디어 시작시각, SegmentTimeline 누적 t/d 또는 n*duration)</param>
    private static string Subst(string template, string repId, string bw, long number, long time)
        => template.Replace("$RepresentationID$", repId)
                   .Replace("$Bandwidth$", bw)
                   .Replace("$Number$", number.ToString())
                   .Replace("$Time$", time.ToString());

    private static Uri Combine(Uri? baseUri, string? rel)
    {
        if (string.IsNullOrEmpty(rel)) return baseUri!;
        if (Uri.IsWellFormedUriString(rel, UriKind.Absolute)) return new Uri(rel);
        if (baseUri == null) return new Uri(rel, UriKind.Relative);
        return new Uri(baseUri, rel);
    }

    private static double ParseDuration(string? d)
    {
        if (string.IsNullOrEmpty(d)) return 0;
        var s = d.Trim();
        if (!s.StartsWith("PT", StringComparison.OrdinalIgnoreCase)) return 0;
        s = s.Substring(2);
        double total = 0; var num = "";
        foreach (var ch in s)
        {
            if (char.IsDigit(ch) || ch == '.') num += ch;
            else if (ch is 'H' or 'M' or 'S' && double.TryParse(num, NumberStyles.Any, CultureInfo.InvariantCulture, out var v))
            {
                total += ch == 'H' ? v * 3600 : ch == 'M' ? v * 60 : v;
                num = "";
            }
        }
        return total;
    }
}